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參數(shù)資料
| 型號： | L4918 |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | VOLTAGE REGULATORS PLUS FILTER |
| 中文描述： | 電壓穩(wěn)壓器和過濾器 |
| 文件頁數(shù)： | 3/6頁 |
| 文件大?。?/td> | 84K |
| 代理商： | L4918 |
ELECTRICAL CHARACTERISTICS
(T
amb
= 25
°
C; V
i
= 13.5V, unlessotherwisespecified)
Symbol
V
i
V
O
Parameter
Test Conditions
Min.
Typ.
Max.
20
8.9
Unit
V
V
Input Voltage
Output Voltage
V
i
= 12 to 18 V
I
O
= 5 to 150 mA
V
i
= 5 to 10 V
I
O
= 5 to 150 mA
V
i
= 12 to 18 V
I
O
= 10 mA
I
O
= 5 to 250 mA
t
on
= 30
μ
s
t
off
=
≥
1 ms
V
i
= 8.5 V
I
O
= 5 to 150 mA
t
on
= 30
μ
s
t
off
=
≥
1 ms
I
O
= 5 mA
V
i
= 6 to 18 V
I
O
= 5 to 150 mA
I
O
= 10 mA
8.1
8.5
V
I/O
Controlled
Voltage
Line Regulation
Input-output
Dropout
1.6
2.1
V
V
O
1
20
mV
V
O
Load Regulation
100
mV
V
O
Load Regulation
(filter mode)
150
250
mV
I
q
I
q
Quiescent Current
Quiescent Current Change
1
2
mA
mA
0.05
V
O
T
SVR
Output Voltage Drift
1.2
mV/
°
C
Supply Voltage Rejection
V
iac
= 1 V
rms
f = 100 Hz
I
O
= 150 mA
V
IDC
= 12 to 18 V
V
IDC
= 6 to 11 V
71
35(*)
300
dB
dB
mA
I
SC
t
on
Short Circuit Current
Switch On Time
250
I
O
= 150 mA
V
i
= 5 to 11 V
V
i
= 11 to 18 V
500(*)
300
150
ms
ms
°
C
T
JSD
Thermal
Temperature
Shutdown
Junction
(*) Depending of the C
FT
capacitor
PRINCIPLE OF OPERATION
During normal operation (input voltage upper than
V
I MIN
= V
OUT NOM
+
V
I/O
). The device works as a
normalvoltageregulatorbuiltaroundtheOP1ofthe
blockdiagram.
The series pass element use a PNP-NPN connec-
tionto reducethe dropout.The referencevoltageof
theOP1isderivedfromaREFthroughtheOP2and
Q3, acting asan active zener diodeof value V
REF
.
In thisconditionthedeviceworks in therange(1) of
the characteristicof thenon linear drop control unit
(see fig.2).
The outputvoltageis fixed to its nominal value:
R1
V
OUT NOM
= V
REF
(1 +
R2
R1
= INTERNALLY FIXED RATIO = 2.4
R2
R1
R2
) = V
CFT
(1 +
)
The ripple rejection is quitehigh (71 dB) and inde-
pendentfromC
FT
value.
Ontheusualvoltageregulators,whentheinputvolt-
age goes below the nominal value, the regulation
transistors (series element) saturate bringing the
system out of regulationmaking it very sensibleto
everyvariationof the input voltage. Onthecontrary,
a controlloop on the L4918consentsto avoid the
saturation of the series element by regulating the
valueof thereferencevoltage(pin2). In fact,when-
evertheinputvoltagedecreasesbelowV
IMIN
thesu-
pervisorloop,utilizing a nonlinear OTA, forces the
referencevoltage at pin2 to decreaseby discharg-
ing C
FT
. So, duringthe staticmode, when the input
voltage goes below V
MIN
the drop out is kept fixed
to about1.6V. In thisconditionthe device worksas
a low pass filter in the range(2) of theOTA charac-
L4918
3/6
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